1. Field of the Invention
This invention relates to flash photography systems, and more particularly to flash photography systems in which an aperture value is determined by preliminary illumination and the amount of main illumination is controlled in accordance with that aperture value.
2. Description of the Prior Art
The electronic flash device in which the aperture of the photographic lens is determined in correspondence to the received amount of the reflection of the preliminary illumination, and the main illumination is controlled at a corresponding critical level to that aperture value, has already been proposed in Laid-Open Patent Application No. SHO 58-102221 in Japan. Also, in this kind of electronic flash devices, there have been previous proposals for using annular illumination coverage varying means in the main flash issuing portion alone, or in combination with another angular illumination coverage varying means in the preliminary light issuing portion. In the latter case, the angle of illumination coverage by the preliminary light issuing portion is made to vary in response to operation of varying the angle of illumination coverage of the main flash light issuing portion so that the preset aperture value by the preliminary illumination always coincides with the electronic flash photographable range of the main illumination. Yet, the aforesaid main illumination coverage angle varying means and the aforesaid preliminary illumination coverage angle varying means of the conventional device each are constructed by an optical member such as a lens, or diffusion plate provided in front of the light issuing portion, and the optical member of the aforesaid preliminary light issuing portion is arranged to move in response to the illumination coverage angle varying means when the aforesaid optical member of the main light issuing portion moves.
Meanwhile, the size of the main light issuing portion itself in this kind of electronic flash device is very large compared with the preliminary light issuing portion. So, the aforesaid movements of the main and preliminary light issuing portions are largely different from each other. Therefore, a problem arose that there was need to use a very complicated linking mechanism between the illumination coverage angle varying means of the main light issuing portion and that of the preliminary light issuing portion.